Conventional coaxial dual-rotor model helicopters such as those disclosed in PCT publication no. WO 02/064425 A2 and Chinese publication No. CN1496923A include two rotors installed on a shaft, one for veer control and another for balance control. Maneuverability and stability mainly depend on whether the balance mechanism adopts balance paddles (WO 02/064425 A2) or balance weights (CN1496923A). Those adopted the balance paddle mechanism have superior balance and veer control but inferior stability, while those adopted the balance weight mechanism have improved stability but poor maneuverability, which are more suitable for novices at aviation models. However, both of the aforesaid structures have a great number of elements, malfunction frequently occurs. Moreover, design for coordination of upper and lower rotors is more sophisticated, and more adjustment parameters are needed and adjustment is complicated. Thus the costs are higher and usability is lower.
As the performances of the aforesaid toy helicopters vary in extremes, either has a great stability or a great maneuverability, they are suitable only for novices or players with experience or professional skills, but not desirable for midrange players who have limited experience but not yet reached the professional level. In short, there is still a need for a midrange model helicopter both in terms of stability and maneuverability in the present market that is yet to be fulfilled.